[Lil' Lavery]

You can hold up to about 70-80 teams on one field (the size of a champ division) and still get a reasonable amount of matches to play.
But the duel field allows some of the larger and growing regionals (Greater Toronto, VCU, ect.) to play more teams and more matches. The biggest problem is not organization, its space. Many venues sqeez to pack in the pits and one field. The only way to add another would be to have a smaller field, or to move the pits to another part of the venue (which most agree is a bad idea).
Pro Venues have enough space to hold multiple fields, but most of the regionals are primarily sponsored by colleges, which typically lack an affiliation with a professional size venue. If we see large corporations start to sponsor regional events, or even sports teams (which with the exception of St. Louis, which the owners of the St. Louis Blues are personally financing, we probably wont see) start to sponsor the regionals then we could move into the pro venues.